Adaptation and plasticity of animal communication in fluctuating environments.

Adaptations that facilitate the reception of long-range signals under challenging conditions are expected to generate signal diversity when species communicate in different habitats. Although we have a general understanding of how individual communicating animals cope with conditions influencing signal detection, the extent to which plasticity and evolutionary changes in signal characteristics contribute to interspecific differences in signaling behavior is unclear. We quantified the visual displays of free-living lizards and environmental variables known to influence display detection for multiple species from two separate island radiations. We found evidence of both adaptive evolution and adaptive plasticity in display characteristics as a function of environmental conditions, but plasticity accounted for most of the observed differences in display behavior across species. At the same time, prominent differences between the two island radiations existed in aspects of signaling behavior, unrelated to the environment. Past evolutionary events have therefore played an important role in shaping the way lizards adjust their signals to challenges in present-day environments. In addition to showing how plasticity contributes to interspecific differences in communication signals, our findings suggest the vagaries of evolution can in itself lead to signal variation between species.